The present invention relates generally to an electrical circuit, for cooperation with a set of noise sensitive electrical instruments and a computer to provide a stand-alone noise testing device. The circuit, according to a predetermined schedule of actuation or variation, and at predetermined time intervals, accepts and processes output signals from the test instruments for subsequent analysis by the computer.
It is preferred that the present circuit be implemented as a single circuit board, and be locatable as an auxiliary unit in a suitable space or expansion slot of the computer. The circuit itself provides multipath, bi-directional communication, preferably through a single first plug/socket unit connection, with the PC, and further multipath, bi-directional communication, preferably through a single second plug/socket unit connection, with a set of test instruments. Preferably as many functions as possible are allotted to the standard facilities of the interconnected personal computer (PC) so that multi-pin plug and socket means may be used to communicate between the circuit board and the PC. Since various control signals required may be non-standard, these non-standard signals may be generated from unused standard address signals available from most PCs. Certain functions such as a clock, oscillator or keying signal may also be included as part of the present circuit for flexibility in adapting to certain PCs when these have non-standard locations or connector terminals for sources of these signals. The display facilities of the PC can be used to display test data, but the X and Y signals displayed may be analog signals derived either from certain address signals or from the instruments and their controls.
One application of the present invention is testing gearboxes, such as heavy duty truck transmissions, for excessive noise or particular noise characteristics. A principal embodiment of the invention reads instruments, set up to sense varying test conditions in a machine, feeds X-Y signals to the computer for defining graphs, and processes and feeds to the computer signals derived from progressively varying readings of the instruments. The embodiment enables various frequency components to be analyzed, and preferably enables Fourier analyses to be graphed and displayed, stored or printed.
Noise is becoming an increasingly bothersome hindrance to human comfort, and the most irritating frequency components and hence, sources of the noise can often be discovered by signal processing. Prior devices of this type involve the measurement of all noise over a very wide acoustic band, or of a continuous given audio band. A feature of the present invention is to observe noise content selectively at points distributed over a given frequency band, to provide a direct portrayal of the potential nuisance quality of machines, either absolutely, or against a standard display deemed to be satisfactory, at some or all of selected frequencies to which the human ear is found or believed to be sensitive, or finds objectionable.
Alternatively or additionally, a machine being tested may have known resonances or cyclic running patterns, e.g. gear tooth meshings, in which case the tests can be directed mainly at specific frequency components and harmonics, or just to selections of these harmonics which are most objectionable to the human ear. Computer power and time are saved if observations of such predictable fundamentals and higher or lower order harmonics and sub-harmonics are focused on. For instance, it is possible to predict the audible frequencies to be expected from a heavy vehicle transmission having a certain number of teeth, ratios and stages, run at various typical or test speeds, under certain controlled torque conditions.
The invention thus provides an auxiliary circuit unit having a first bi-directional multi-path communication connection associated with or mounted thereon, to communicate address words, sensed and quantized instrument data for the displaying signals, and other data or control signals for the instruments. Means to generate supply signals for the measurement instruments and for controlled operation of the signal sources may also be included, such sources being typically noisy machines to be measured. Means are provided to process the instrument output data for communication to the computer via the first communication means. A second bi-directional multi-path communication connection associated with or mounted also on the unit is provided to communicate the control and readout signals between the unit and the instruments or the noise sources.
The signals to be measured henceforth will be referred to as "noise" signals. Such noise may be interesting from a point of view of legal or humanly bearable limits, or from the point of view of detecting breakages, damaged teeth, or over-stressed mechanical parts in a transmission. One preferred test procedure suitable for a factory environment, to test heavy goods vehicle transmissions for excessive noise, the international standards for which are becoming ever more stringent, is the following. The skilled man will readily adapt such tests for different transmissions or machines.
(a) rms (root mean square) noise is measured against rpm (revolutions per minute) at certain required intervals; for example, for intervals of 20 rpm from a minimum 1000 to a maximum 2000 rpm range, and at one or more given torques or for varying torques: PA1 (b) a frequency Fourier analysis is computed in order to ascertain various frequency components contributing unduly to output noise: PA1 (c) these frequency components are measured at 512 frequency steps of 11 Hz, from the very low to 6000 Hz, above which the human ear is less sensitive, the chosen frequency range preferably generally being a compromise, to avoid requirement for excessive testing: PA1 (d) the response curve to these frequencies up to the 6000 Hz limit may be shaped, using an input A-weighted filter, or one similar in sensitivity to that of the average human ear: PA1 (e) the rpm range is a similarly chosen compromise, in that heavy diesel engines rotate predominantly within this range, and often the numbers of teeth and the speed of relative movement of these teeth when in mesh, can be used, calculated, measured or compared to predict where excessive noise is likely: PA1 (g) since most noises are highly frequency dependent due to meshing and unmeshing of cogs with known numbers of teeth and ratios thereof, noise components at these frequencies may be exclusively or mainly investigated, such as by opening windows using appropriate software. For instance we may predict and identify, based on theory for one particular ratio the mesh frequencies of each pair of meshed gears: PA1 (h) excessive noise amplitudes at certain orders can suggest certain faults, damage, over-stress, or distortions which can be individually attended to, or can be motive for rejecting a component, without any necessity to inspect an entire machine: PA1 (i) it should be remembered that most gearboxes seem not to give significant, at least as far as the human ear is concerned, noise components above 4000 Hz, even at high revolution rates, but there may well be many exceptions; the experience of 4000 Hz being a practical ceiling for appreciable noise, is a motivation for investigating components only up to 6000 Hz: PA1 (j) any of these analyses may be preferably performed for one or more typical or highest torques, for each one of 18 or so gear ratios engaged: PA1 (k) when predicting theoretically, presently preferred is to "consider" the fundamental and the next three harmonics; by "consider" we mean as analyzed at the 512 discreet frequencies.
(f) having regard to the known propensity for a particular gearbox model, a standard response curve for a good sample is compared with that of the test sample, for each rpm speed, frequency component and torque of interest:
It is often desirable that some of the various parameters such as rpm be swept through quite rapidly, preferably not continuously, but in steps, which can be regular intervals or chosen steps where resonances are anticipated or already measured once, or associated with a particular design; and computer measurements and Fourier analyses registered and stored, for examination off-site, after the machinery has been stopped.
A single board embodiment of the present invention will now be described, designed for incorporation into a PC in order to cooperate therewith to provide a self-sufficient noise testing apparatus, which can provide a Fourier analysis and easily read indications of pass or fail without requirement for detailed portrayal of the intermediate analyses.
Other advantages and features of this invention will become apparent form the following specification taken in conjunction with the accompanying drawings.